Dr. Joan Bartra: “Although we are getting better at controlling allergic disease, we are still a long way from finding a cure”

Respiratory allergy affects around 25% of the general population, especially in spring, at the height of the pollen season. We talk to Dr. Joan Bartra about the most common allergies and why they occur.

What is respiratory allergy?

It is an inflammation of the airways, starting with the nose and eyes, and it can also affect the bronchi. The inflammation of the nose is known as rhinitis, the inflammation of the eyes is conjunctivitis, and when the bronchial tubes become inflamed this is asthma. When we speak of respiratory allergy, we are referring to rhinoconjunctivitis or asthma. Moreover, it is common for both to appear in the same patient.

What are the most common allergens that cause respiratory allergies?

In our geographic area, dust mites. Coastal and pre-coastal areas have high humidity and mild temperatures, which mean the mite's life cycle is much more active.

Other common allergens are dander and pet hair, usually that of cats and dogs but also guinea pigs, for example. With regard to dander, the allergy is produced by the proteins found in the animal’s hair, dead skin cells, urine and saliva. The concentration can vary, depending on the protein.

There is also pollen allergy; allergy to tree or grass pollens. In the case of trees, in our area it involves species in the family Cupressaceae, such as the cypress. Allergies to plane tree pollen and olive tree pollen are also common. When it comes to grasses, those that have seeds, such as wheat, are the main culprits. Also weeds such as wall pellitory, which belongs to the nettle family.

Changes in the pollination rate due to climate change or the presence of non-native plants, which were not present years go, are factors that influence pollen allergy.

Are new allergens appearing? What is the effect of climate change?

New allergens are appearing, or more of the existing ones, because of the new policy of ornamental trees in cities, for example. In recent years, we might have found pollens that were not present in our area before. For example, in the city of Barcelona we can find ornamental plants belonging to the olive family (Oleaceae) that grow more easily here. The proteins in the pollen of these plants are responsible for many respiratory allergies.

Changes in the pollination rate due to climate change or the presence of non-native plants, which were not present years go, are factors that influence pollen allergy. As we are able to see what we are breathing in thanks to aerobiology – the science that studies airborne particles – we see that there might be new respiratory allergy triggers.

For example, another allergen is fungal spores. Whilst pollens follow a similar distribution each year, fungal spores can behave far more erratically. In 24-48 hours, they can increase by over 1,000% because they are greatly influenced by atmospheric conditions.

Why do allergies sometimes appear after a few years of being in contact with the allergen?

We don’t know why. No one is born with allergies. There may be a certain predisposition, and then there must be an alteration in the immune system caused by sustained or sporadic contact with the allergen. For an allergy to occur, there must be a sensitization phase, which means having been in contact with the allergen without any reaction. At a certain point, the allergic reaction begins. We do not know when it starts to develop. There is no biomarker to tell us, because some patients never have an allergic reaction and others do, and at very different ages.

There is currently a revolution in the treatment with biological drugs, which inhibit all the molecules involved in the inflammatory immune response.

What happens inside the body when an allergy appears?

The immune system fights off foreign substances when it should not be doing so. Be it pollens, mites, food, drugs or bee or wasp venom. When the allergen, which is a protein, enters the body, defence mechanisms (IgE antibodies) are generated and bind to the surface of certain cells. When activated, they release substances such as histamine or tryptase, which trigger all the symptoms of the allergic reaction. When anaphylactic shock occurs, there is a massive release that affects the cardiovascular system, which becomes decompensated, or affects the respiratory system that collapses creating a life-threatening situation.

Where is research heading?

Where a real revolution is currently taking place is in the treatment with biological drugs, which inhibit all the molecules involved in the inflammatory immune response. New vaccines are also being developed. This is the only treatment that is currently capable of changing the natural course of the disease. The vaccines “reset” the immune system, so that the production of antibodies against foreign proteins does not occur, or it occurs in smaller quantities. They can also cause other antibodies to appear that neutralize the antibodies causing the allergic reaction (IgE). There have been patients who have suffered anaphylactic shock following stings from Hymenoptera (such as bees or wasps), and, after a few months of treatment with vaccines, have experienced no reaction to new stings, or only a very mild reaction. These are patients who were on the verge of losing their life. This shows how effective vaccines can be.

Why is all this allergy stuff so complicated?

In order to understand an allergy, you need to know the trigger or allergen, which is the X factor in the equation. The Y factor is what happens inside the individual. However, the allergic reaction is not always the same in terms of severity, because many other factors that are hard to control can also be involved. This means that when a person is exposed to the same allergen, sometimes they may have more severe clinical manifestations and other times they will not be so severe. This is perhaps because the quantity of the allergen is different, or because the person’s hormones are different.

When an allergy occurs, it means there is an imbalance; an immunological homeostasis involving many agents has been disrupted. Given the complexity of this alteration, the mechanisms for reversing it are also complex, and hopefully one day we will be able to cure it. We are learning more and more about the triggers of allergic reactions. Therefore, if we know what causes them, we can give preventative advice. Drugs have also been developed that help control the symptoms and have few or no side effects. The control of allergic disease is becoming increasingly possible and effective. However, we are still a long way from finding a cure.

Image: Dr. Joan Bartra. Allergist. Doctor at the Hospital Clínic Pulmonology and Respiratory Allergy Service, Senior Researcher in the IDIBAPS Clinical and Experimental Respiratory Immunoallergy Group (IRCE), and Associate Professor at the University of Barcelona.